A trickling filter is a biochemical wastewater treatment process, which relies on microorganisms growing in the surface film on the rock media to assimilate the biodegradable organic substances in the wastewater as it trickles down. Having an adequate supply of fresh air in the void spaces within the rock media is of critical importance to its successful operation.
During the operation of the filter, microorganisms, which are naturally present in the wastewater, establish a gelatinous microbial film on the surface of the media. As the wastewater trickles down past the microbial mass, the microorganisms consume the biodegradable organic matter, thus purifying the wastewater. As the microorganisms grow and multiply, the microbial film thickens and sloughs off the surface of the media. Part of the microbial film is constantly being carried out of the filter by the wastewater. The microbial population established on the surface of the media requires oxygen to thrive and to provide their wastewater purification functions. If there is insufficient air flow through the filter media, the treatment performance decreases, and odorous conditions develop.
Traditionally, the only means of providing oxygenated fresh air has been by air circulation due to natural draft; i.e., air movement caused by the temperature differential between the wastewater and the ambient air. When the wastewater is warmer than the ambient air, the wastewater warms the air, causing it to rise through the rock media and to the atmosphere. When the wastewater is cooler than the ambient air, the wastewater cools the air, causing it to travel downwards through the rock media and out of the filter through vents, access shafts, and the like. It has been estimated that in order for there to be adequate air movement through trickling filter rock media, the temperature difference between the ambient air and the wastewater must be in the order of 10.degree. F. to 15.degree. F. Without adequate air movement, the oxygen transfer from the air to the wastewater is not sufficient to maintain the aerobic conditions required by the microbial population growing on the surface of the rock. As a result, anaerobic conditions are created in the filter, the wastewater treatment performance is adversely affected, and odorous gases are produced. Eventually when the relative temperatures of the ambient air and the wastewater become conducive to higher air movement through the filter media, the odorous gases accumulated are released to the atmosphere, creating the potential for odor complaints from the surrounding community and penalties from the regulatory agencies.
In some instances, odor-laden gases from rock media trickling filters have been captured by covering the filter with a dome and withdrawing the gases from under the dome by suction. The gases can then be exhausted to the atmosphere directly or after treatment with odor-control equipment. If there are places for fresh air to enter the filter underdrain, so it can flow upwards through the rock media, this method should enhance the aeration of the wastewater.
Another method, which has been conceived to improve the aeration of the wastewater involves covering the filter with a dome and forcing air into the dome, so it flows through the filter media and filter underdrain, and is exhausted to the atmosphere through the filter effluent channel or pipe, filter vents, and the like. However, this method has the drawback of not providing for readily capturing the gases for subsequent odor-control treatment.
Conventional filters cannot always provide sufficient aeration of the wastewater, since air flow through the filter is dependent on atmospheric conditions, which are beyond the control of the filter operator. As a result, conventional filters typically release gases of an obnoxious character, which create nuisance odor conditions in the surrounding areas.
Prior patents in this field have also failed to provide satisfactory results. For example, U.S. Pat. No. 3,275,147 shows a system for a trickling filter where there is a plastic dome covering the filter bed and a blower is used to produce pressurized air which is forced down through the filter media bed to produce wet scrubbing of the odor-laden air over the entire bed of filter material. However, this patent does not provide a downward air flow caused by a negative air pressure to insure that odorous gases are not created and sent into the atmosphere. The following prior art patents also do not have downward air flow caused by a negative air pressure in regard to trickling filters:
U.S. Pat. Nos.: 947,333 PA1 2,200,581 PA1 3,126,333 PA1 3,853,752 PA1 3,966,599 PA1 4,631,183 PA1 5,030,353
It is an object of the present invention to provide a trickling filter system which positively insures that a downward air flow through a filter media bed is created by a negative air pressure apparatus which insures that malodorous gases are not created and sent into the atmosphere.
Another object of the present invention is that it provides a downward flow of air through the filter media bed and thereby provides a sufficient and continuous supply of oxygen to maintain the necessary aerobic conditions for the microorganisms to grow and biodegrade the organic matter in the waste water treated in said trickling filter.
A further object of the present invention is to provide a scrubber system in cooperation with the trickling filter, so that the reacted air exiting from the filter media and ventilation systems are directed to the scrubber system to remove any remaining noxious or malodorous gases before said reacted air is released to the atmosphere.